Clayton began covering sports while still a student at Churchill Area High School. Starting with the Pittsburgh Steelers' 1972 training camp, he covered the team in twice-weekly dispatches in the St. Marys, Pennsylvania Daily Press. He later wrote for Steel City Sports, a weekly publication in Pittsburgh. In 1975, Steel City Sports changed into Score! Pittsburgh and Clayton was a staff writer, covering the Steelers. He also served as a stringer for a number of radio networks, including AP Radio, and covered games, providing the network with sound clips from locker room interviews after games involving Pittsburgh's professional sports teams.
Clayton graduated from Duquesne University in 1976, and later worked for The Pittsburgh Press. He had done part-time work for the paper while attending college.
In May 1978, Clayton was sent to cover a Steelers mini-camp in place of the Press' regular Steelers beat writer, Glenn Sheeley. While there he discovered and reported a rules violation which would cost the team a draft pick. The affair was dubbed "Shouldergate" by Clayton. Clayton became persona non grata for some time in his hometown for his role in the affair.
Clayton eventually worked his way up to become the Steelers beat writer at the Press, before leaving the paper in 1986. He moved across the country and began covering the Seattle Seahawks for The News Tribune in Tacoma, Washington. It was at this time that he began appearing in NFL segments on Seattle sports radio station KJR (AM) on host Nanci Donnellan's program "The Fabulous Sports Babe". When Donnellan's show was picked up by ESPN for national syndication, Clayton came along as an NFL correspondent.
In 1995, Clayton joined ESPN as a reporter and later added to his duties a weekly radio show during the NFL offseason. He hosted the show with former NFL quarterback Sean Salisbury; the show included "Four Downs," a debate with Salisbury over current NFL issues. Their debates often became quite heated, with Salisbury referring to Clayton as the "Cryptkeeper" and "Mr. Peabody", mocking his geeky and "eggheaded" appearance and voice, and Clayton responding by calling Salisbury "Mr. Backup" based on his limited playing time during his NFL career. There is debate as to seriousness of the animosity between Salisbury and Clayton. He was let go from ESPN on May 31, 2017.
Clayton remained a frequent contributor to KJR (AM), and hosted its "Sports Saturday" show on Saturday mornings. He is a regular caller to sports-talk radio stations around the country. Because of the transition to all-sports of KIRO (AM) Seattle, Clayton moved his show to the new ESPN station.
Clayton received the Dick McCann Memorial Award from the Pro Football Hall of Fame in 2007. This distinction puts him in the "writer's wing" of the Hall of Fame.
He was also inducted into the sports hall of fame of his alma mater, Duquesne University, in 2001.